Wetland-microbial Fuel Cell System Research Articles

An integrated constructed wetland-Microbial fuel cell system with sewage sludge-biochar to enhance treatment and energy recovery efficiencies

Constructed wetlands and microbial fuel cells (CW-MFCs) are a promising green and sustainable wastewater treatment technology. However, the power production performance of CW-MFCs has long been limited by low-performance cathodes. In this study, we designed two CW-MFC systems using cheap and readily available sewage sludge biochar (SSB) as the substrate for the experimental units. The integration of SSB significantly facilitated the removal of chemical oxygen demand, ammonium nitrogen, total nitrogen, and total phosphorus. Moreover, SSB enhanced the electrochemical performance of the air cathode, resulting in higher power density (44.64 mW/m2) and lower internal resistance (900.00 Ω) compared to gravel-integrated CW-MFC (0.88 mW/m2, 2057.14 Ω). In addition, a typical electroactive bacterium---Geobacter was enriched in the SSB-integrated CW-MFC system. The iron oxides and graphic nitrogen of the SSB favor the growth of Geobacter, and the redox-active groups on the surface of SSB accelerate the extracellular electron transfer process, contributing to the enhancement of treatment performance. Meanwhile, the metal and nitrogen doping improves the oxygen reduction reaction activity and conductivity of SSB, enhancing the cathode area of CW-MFC and improving the energy recovery. Overall, these results demonstrated that SSB-integrated CW-MFC can be a competitive technology for effective wastewater treatment and energy recovery.

Cost benefit analysis of integrated constructed wetland microbial fuel cell system for sustainable and economic domestic wastewater treatment

Wastewater treatment with integrated constructed wetland–microbial fuel cell technology has attracted serious attention from researchers. The economic sustainability of any potential technology is the key to its commercialization from laboratory to field application, which is fulfilled through an exhaustive assessment of the related costs and benefits. This article presents a comparative cost-benefit analysis of three reactors: constructed wetland (R1), integrated CW-MFC (R2), and unplanted CW-MFC (R3) for domestic wastewater treatment and economic sustainability assessment. The study was conducted with 36 h and 24 h hydraulic retention times of the reactors and the respective cost-benefit ratio was determined. Results revealed that R2 was the most sustainable option with maximum economic benefits during Phase 1 and Phase 2 without effluent disinfection. With effluent disinfection in place, R1 emerged with the best cost-benefit ratio due to less investment cost and low revenue from electricity production in R2 and R3. Sensitivity analysis with net investment cost, power density, electrode area, effective reactor volume, and hydraulic retention time; showed power density was the most influential parameter affecting the cost-benefit ratio. Revenue from wastewater treatment was found essential for economic sustainability which shows the importance of producing high-quality effluent and greater power density to make CW-MFC technology economically attractive.

Innovative pyrite-based constructed wetland-microbial fuel cell for enhancing nutrients removal and bioelectricity generation

Anode filler of constructed wetland-microbial fuel cell system (CW-MFC) was proven to have a huge impact on nutrients removal and bioelectricity generation. This study set up an innovative pyrite-based constructed wetland-microbial fuel cell (PCW-MFC) and further investigated the effect of pyrite filler on nutrients treatment efficiency, bioelectricity generation performance and functional microbial communities compared to conventional CW-MFC and PCW. The results showed that the overall processing performance of PCW-MFC was better than that of CW-MFC and PCW systems. The average removal efficiency of COD, NH4+-N, NO3−-N and TP in PCW-MFC was 88.79 ± 0.95 %, 80.39 ± 0.75 %, 89.43 ± 0.76 % and 60.49 ± 1.39 %, respectively. Meanwhile, the maximum output power density of PCW-MFC reached 123.16 mW/m3, which was 11.6 % higher than the maximum output power density of CW-MFC (110.36 mW/m3). The maximum output voltages for both were 0.478 V and 0.421 V, respectively. According to microbial community analysis, pyrite promoted the enrichment of the genera (Dechloromonas, Acinetobacter, and Thiobacillus) associated with nitrogen and phosphorus removal and the exoelectrogen Geobacter which made PCW-MFC have better electricity generation performance. This study provided ideas and theoretical support for developing and improving the performance of CW-MFC fillers.

Performance optimization of two-stage constructed wetland-microbial fuel cell system for the treatment of high-concentration wastewater.

Constructed wetland-microbial fuel cell (CW-MFC) has attracted much attention because of its dual functions of wastewater treatment and energy recovery. However, its performance in treating high-concentration wastewater is degraded by the decreased dissolved oxygen at the cathode and insufficient electron acceptors. In this study, two CW-MFC systems with cathodic aeration were connected in series to investigate the effects of aeration rate and hydraulic retention time (HRT) on the removal of pollutants and the performance of electricity production in high-concentration wastewater. Results showed that aeration enhanced NH4+-N and TP removal by 45.0-49.8% and 11.5-18.0%, compared with the unaerated condition, respectively. Meanwhile, no significant change regarding COD removal was observed. Aeration enhances the output voltage and power density of the system, especially the first stage CW-MFC, which improved the power production performance by 1 to 2 orders-of-magnitude. Increasing HRT improves the system's pollutant treatment efficiency and power generation performance for high-concentration wastewater. Still, the extension of HRT to 2days will not contribute much to improving the removal efficiency. Under optimized conditions, the maximum total removal rates of COD, NH4+-N, and TP for the two-stage tandem CW-MFC system were 99.3 ± 0.2%, 92.4 ± 1.6%, and 79.5 ± 3.4%, respectively. Meanwhile, the maximum output voltage and maximum power density of the first-stage CW-MFC were 405mV and 138.0mW/m3, respectively. In contrast, the maximum output voltage and maximum power density of the second stage are 105mV and 14.7mW/m3, respectively.

Effect of External Aeration on Cr (VI) Reduction in the Leersia hexandra Swartz Constructed Wetland-Microbial Fuel Cell System

Cr (VI) is hazardous to humans and our environment. Leersia hexandra Swartz (L. hexandra) is the first wet chromium hyperaccumulator found in China. This study constructed the L. hexandra constructed wetland-microbial fuel cell (CW-MFC) system to treat Cr (VI) wastewater. It also determined the effects of different dissolved oxygen (DO) concentrations on power generation, pollutant removal, and Cr (VI) reduction. Cathode aeration promoted the voltage output and pollutant removal of the L. hexandra CW-MFC when the DO concentration was 4.5 mg·L−1: the highest voltage was 520 mV, the chemical oxygen demand (COD) removal rate was 93.73%, and the Cr (VI) removal rate was 97.77%. Moreover, the increase in the DO concentration improved the absorption of heavy metal Cr by the substrate and L. hexandra, and promoted the transformation from Cr (VI) to Cr (III). Chromium mostly exists as a residue with low toxicity and low mobility in L. hexandra and the substrate. This proves that the increased DO concentration promotes the redox reaction in the system and plants, reducing Cr (VI) to Cr (III). At the same time, the key micro-organism Geobacter that enhances the performance of the system and Cr (VI) reduction was found. The research results can provide a reference for the subsequent CW-MFC treatment of actual Cr-containing wastewater.

Innovative pilot-scale constructed wetland-microbial fuel cell system for enhanced wastewater treatment and bioelectricity production

In this study, a unique configuration of pilot scale constructed wetland-microbial fuel cell (CW-MFC) system was evaluated in terms of chemical oxygen demand (COD) removal from synthetic wastewater and bioelectricity generation. The system consists of nine individual CW-MFC units and two aerobic chambers configured in a fibre-reinforced rectangular tank (Total working volume-135.5 L). Typha angustifolia was used as wetland plant. To enhance electrical performance of the system, two auxiliary MFCs equipped with terracotta-based separator-electrode-assembly (SEA) were integrated into the anodic zone of each CW-MFC unit in addition to the conventional sediment-configured MFC. The system was evaluated in fed-batch and continuous up-flow modes of operations. All the CW integrated MFCs were studied individually without any combinations (parallel/series). In fed-batch mode, the CW-MFC unit of the system removed a maximum of 97.56 ± 1.6 % of COD from wastewater. The highest power and current densities achieved by the auxiliary MFCs were 58.55 mW/m2 and 229.6 mA/m2 respectively. In the continuous up-flow mode, the pilot-scale system treated around 4100 L of wastewater and exhibited a maximum of 82.8 ± 1.9 % COD removal efficiency. Whereas, the auxiliary MFCs attained the maximum power and current densities of 41.44 mW/m2 and 283.3 mA/m2 respectively. In both modes, the internal resistance of the auxiliary MFCs was found to be two times lower than that of the conventional sediment-configured MFCs of the system. The overall results manifested that the inclusion of SEAs and aerobic chambers in this innovative pilot-scale CW-MFC shows merit and improved the energetics of the system.

Curbing per- and polyfluoroalkyl substances (PFASs): First investigation in a constructed wetland-microbial fuel cell system

The presence of per- and polyfluoroalkyl substances (PFASs) in water environments has been linked to a slew of negative health effects in both animals and humans, but the green and eco-sustainable removal technologies remain largely unknown. Constructed wetland coupled microbial fuel cell (CW-MFC) is termed a “green process” to control pollutants and recover energy. However, so far, no study has investigated the removal of PFASs and their effects on the performance of the CW-MFC systems. Here, we investigated the removal performance of PFOA and PFOS in the CW-MFC systems both in the absence and presence of electricity circuit, and explored the distribution and fate of PFASs and their interactions with other elements in the systems. Our findings demonstrated excellent removal efficiency of >96% PFOA and PFOS in CW-MFC systems. PFOA and PFOS were distributed throughout the system via wastewater flow, while electrode material and plants are the main enrichment sites in which MFC enhanced up to 10% PFASs removal. However, a loss of 7.2–13.5% of nitrogen removal and a decrease of 7.3% in bioelectricity output were observed when PFASs were introduced in the system. The driven force led to the loss of nitrogen removal and bioelectricity generation lies in the accumulation of PFASs in system composition, which affected microbial activity and community composition, damaging the health of the plant, and in turn reducing CW-MFC's functioning. No doubt, CW-MFC systems provide an alternative technique for PFASs removal, alleviating some limitations to the physical and chemical techniques, but further investigation is highly needed.

Saturated constructed wetland-microbial fuel cell system and effect on dissolved oxygen gradient, electricity generation and ammonium removal

ABSTRACT The aim of this work was to assess effect of saturated constructed wetland-Microbial fuel cell system on dissolved oxygen gradient, electricity generation and ammonium removal. Two laboratory-scale systems, one planted with Schoenoplectus californicus (SCW1-MFC) and other without plant (SCW2-MFC), were fed discontinuously with synthetic wastewater over 90 days. Both systems were operated at different organic loading rate (12 and 28 g COD/m2d) and ammonium loading rate (1.6 and 3.0 g NH4 +– N/m2 d) under open circuit and close circuit mode. The results indicate that between lower and upper zones of wetlands the average values were in the range of 1.22 ± 0.32 to 1.39 ± 0.27 mg O2/L in SCW1-MFC and 1.28 ± 0.24 to 1.56 ± 0.31 mg O2/L in SCW2-MFC. The effect of operating mode (closed and open circuit) and vegetation on DO was not significant (p > 0.05). Chemical oxygen demand (COD) removal efficiencies, fluctuated between 90 and 95% in the SCW1-MFC and 82 and 94% in the SCW2-MFC system. Regarding NH4 +- N, removal efficiencies were above 85% in both systems reaching values maximus 98%. The maximum power density generated was 4 and 10 mW/m2 in SCW1-MFC, while SCW2-MFC recorded the highest values (12 and 22 mW/m2).

Performance optimization and microbial community evaluation for domestic wastewater treatment in a constructed wetland-microbial fuel cell

Constructed wetland-microbial fuel cell system (CW-MFC), an attractive technology still under study, has shown to improve domestic wastewater treatment efficiency and generate bioelectricity. This work investigated the effect of multiple factors on the performance optimization for the pollutants removal and bioelectricity production compared to a traditional CW, including influent chemical oxygen demand (COD) concentration, hydraulic retention time (HRT) and external resistance. The results showed that the optimal operating conditions of COD concentration, HRT and external resistance for CW-MFC were 200 mg/L, 24 h and 1000 Ω, respectively. The average COD, NH4+-N, NO3--N and TP removal efficiencies were 6.06%, 3.85%, 3.68% and 3.68% higher than these in CW system, respectively. Meanwhile, the maximum output voltage and power density of CW-MFC were 388 ± 12 mV and 107.54 mW/m3. In addition, the microbial community analysis indicated that the pollution removal and bioelectricity generation might benefit from the gradual enrichment of electroactive bacteria (Tolumonas) and denitrifying bacteria (Denitratisoma, Methylotenera and Sulfuritales). The findings can provide the optimum operation parameters and mechanism insight for the performance of CW-MFC systems.

Insight into the performance discrepancy of GAC and CAC as air-cathode materials in constructed wetland-microbial fuel cell system

Constructed wetland-microbial fuel cell (CW-MFC) has exhibited the performance discrepancy between using granular activated carbon (GAC) and columnar activated carbon (CAC) as air-cathode materials. No doubt, this is linked with electrochemical performance and decontaminants characteristics in the CW-MFC system. To provide insight into this performance discrepancy, three CW-MFCs were designed with different carbon-material to construct varied shapes of air-cathodes. The results showed that the ring-shaped cathode filled with GAC yielded a highest voltage of 458 mV with maximum power density of 13.71 mW m−2 and >90% COD removal in the CW-MFC system. The electrochemical characteristics and the electron transport system activity (ETSA) are the driven force to bring the GAC a better electron transportation and oxygen reduction reaction (ORR). This will help elucidating underlying mechanisms of different activated carbon for air-cathode and thus promote its large application.

Effect of drained-flooded time ratio on ammonia nitrogen removal in a constructed wetland-microbial fuel cell system by tidal flow operation

A novel constructed wetland-microbial fuel cell system by tidal flow operation (TFCW-MFC) was constructed to intensify ammonia nitrogen removal. The nitrogen removal performance of the TFCW-MFC with different ratios of drained and flooded time (D/F ratios) was investigated to determine the optimal operating strategy. The highest TN removal efficiency of 52.89 ± 3.16% was obtained at the D/F ratio of 1:5 (C/N ratio: 5). The bacterial communities in the anode (granular activated carbon and graphite felt, referred to as TF_a1 and TF_a2, respectively) and the cathode (graphite felt, referred to as TF_c) collected from the TFCW-MFC were characterized using 16S rRNA gene high-throughput sequencing technology. The high abundance of Nitrospira predominant in the anode indicated that the tidal flow operation strengthened the system's reoxygenation ability, thus improving the overall nitrification efficiency of the system. Besides, Acinetobacter (21.67%) in the cathode could play an important role in the heterotrophic aerobic denitrification process.

Mechanism involved in the treatment of sulfamethoxazole in wastewater using a constructed wetland microbial fuel cell system

A constructed wetland (CW) and a constructed wetland microbial fuel cell (CW-MFC) were used for 70 d to remove sulfamethoxazole from wastewater. The amount of sulfamethoxazole removed, extracellular polymer content, microbial community evolution, and changes in the abundances of genes related to antibiotic resistance were assessed. The total nitrogen, ammonia nitrogen, and sulfamethoxazole removal efficiencies were significantly (P < 0.05) higher (6.87%, 21.07%, and 11.05% higher, respectively) for the CW-MFC than the CW. Good removal efficiencies and the power generation performance indicated that the CW-MFC was more stable than the CW in the presence of sulfamethoxazole. The extracellular polymer content was lower for the CW-MFC than the CW. The phylum Proteobacteria was dominant in the CW-MFC. High Pseudomonas concentrations in the CW would have caused organic matter decomposition but not electricity generation. The Methylotenera content was 4.5 times higher in the CW-MFC anode than the CW anode. Methylotenera are able to perform denitrification and could have caused the high nitrogen removal rate for the CW-MFC. The sulfamethoxazole resistance gene copy number was much higher for the CW than the CW-MFC, indicating a higher risk of antibiotic resistance genes spreading in the CW than the CW-MFC. The results indicated that the CW-MFC is a promising technique for removing sulfamethoxazole from wastewater that offers environmental and economic benefits over alternative methods.

Organic matter removal and nitrogen transformation by a constructed wetland-microbial fuel cell system with simultaneous bioelectricity generation

Microbial fuel cells integrated into constructed wetlands have been previously studied. Nevertheless, their application as a suitable treatment for wastewater is still in the developmental stage.In this context, the aim of this study was to evaluate organic matter removal and nitrogen transformation by a microbial fuel cell integrated into a constructed wetland (CWMFC). To accomplish this, three experimental systems were operated under batch-mode conditions over 170 days: i) one was planted with Schoenoplectus californicus (P-CWMFC); ii) another was unplanted (NP-CWMFC); and iii) the third system did not have any electrodes (CW) and was used as a control.Chemical oxygen demand (COD) removal efficiency ranged between 74–87%, 69–81% and 62–72% for the P-CWMFC, NP-CWMFC and CW systems, respectively, with organic loading rates (OLR) ranging from 4.8 to 7.9 g COD/m2 d. NH4+-N removal efficiency exceeded 98%, 90% and 83% for P-CWMFC, NP-CWMFC and CW, respectively. Wastewater treatment performance was improved due to anaerobic oxidation that occurred on the anodes. Organic matter removal was 18% higher in closed-circuit mode than in open-circuit mode in both integrated systems (P-CWMFC and NP-CWMFC), and these differences were significant (p < 0.05). With respect to the performance of microbial fuel cells, the maximum power density (8.6 mW/m2) was achieved at an organic loading rate of 7.9 g COD/m2 d with an internal resistance and coulombic efficiency of 251 Ω and 2.4%, respectively. The results obtained in this work can provide positive impacts on CW development by enhancing anaerobic degradation without forced aeration.

Nutrient Removal Process and Cathodic Microbial Community Composition in Integrated Vertical-Flow Constructed Wetland - Microbial Fuel Cells Filled With Different Substrates.

An integrated vertical-flow constructed wetland-microbial fuel cell system (CW-MFC), consisting of an up-flow chamber and a down-flow chamber, was constructed to treat synthetic sewage wastewater. The performance of CW-MFCs filled with different substrates [i.e., ceramsite (CM-A), quartz (CM-B), and zeolite (CM-C) granules] under various hydraulic retention times (HRTs, 7.6, 4.0, and 2.8 d) was evaluated. Efficient and stable nitrogen (N) and phosphorus (P) removals were observed in CM-A under different HRTs, while the voltage outputs of the CW-MFCs was greatly reduced as the HRTs decreased. With an HRT of 2.8 d, the ammonium (NH4+-N) and orthophosphate (PO43–-P) removal efficiencies in CM-A were as high as 93.8 and 99.6%, respectively. Bacterial community analysis indicates that the N removal in the cathode area of CM-A could potentially benefit from the appearance of nitrifying bacteria (e.g., Nitrosomonas and Nitrospira) and relatively high abundance of denitrifiers involved in simultaneous nitrification and denitrification (e.g., Hydrogenophaga, Zoogloea, and Dechloromonas) and denitrifying sulfide removal (e.g., Thauera). Additionally, the difference in N removal efficiency among the CW-MFCs could be partly explained by higher iron (Fe) content in milled ceramsite granules and higher abundance of denitrifiers with nitrate reduction and ferrous ions oxidation capabilities in CM-A compared with that in CM-B and CM-C. Efficient PO43–-P removal in CM-A was mainly ascribed to substrate adsorption and denitrifying phosphorus (P) removal. Concerning the substantial purification performance in CM-A, ceramsite granules could be used to improve the nutrient removal efficiency in integrated vertical-flow CW-MFC.

人工湿地–微生物燃料电池系统应用的发展与展望

人工湿地–微生物燃料电池系统应用的发展与展望

Electricity production enhancement in a constructed wetland-microbial fuel cell system for treating saline wastewater

The use of constructed wetlands in combination with microbial fuel cells (CW-MFC) to treat saline wastewater may enhance electricity production by increasing the ionic strength, reducing internal resistance and stimulating microbes to accelerate electron transfer. In this study, salinity did not significantly inhibit the removal of TP and COD, but TN and NH4+-N removal efficiencies during saline wastewater treatment (ST) were significantly lower than during non-saline wastewater treatment (NT). However, salinity significantly increased the power density (16.4 mW m−2 in ST and 3.9 mW m−2 in NT, a 4-fold enhancement) by increasing the electron transfer rate and reducing internal resistance (140.29 Ω in ST and 415.21 Ω in NT). The peptides in extracellular polymeric substances (EPS) acted as electron shuttles to promote the migration of electrons and protons in ST. From start-up to stable operation, though the microorganisms in ST were reduced in diversity relative to NT, the proportion of electrochemically active bacteria (EAB), such as Ochrobactrum, significantly increased (p < 0.05) and gradually predominated in the microbial community.

Eco-electrogenic treatment of dyestuff wastewater using constructed wetland-microbial fuel cell system with an evaluation of electrode-enriched microbial community structures

This work studied eco-electrogenic treatment of real dyestuff wastewater along with characterization of electrode-enriched microbial community structures in Fimbristylis dichotoma planted closed-circuit constructed wetland-microbial fuel cell (CW-MFC) system. The CW-MFC-2 (experimental system) achieved 82.2 ± 1.7% ADMI removal and 70 ± 2% COD reduction; that were found to be 9% and 7.4% higher than the standalone constructed wetland (CW) system (bioremediation control) respectively. Likewise, the CW-MFC-2 system achieved maximum power density of 198.8 mW/m2, which was 85.6 ± 2.47% higher than the CW-MFC-1 system (eco-electricity control). Quantitative reverse transcription PCR (qRT-PCR) assays revealed significant down-regulation of hepatic oxidative stress response biomarker genes in Oreochromis niloticus exposed to CW-MFC-2 system treated dyestuff wastewater as compared with untreated wastewater. The biofilms associated with the anode and cathode of the CW-MFC-2 system exhibited selective enrichment of electrochemically active and dye degrading microbial communities.

Bioenergy generation and rhizodegradation as affected by microbial community distribution in a coupled constructed wetland-microbial fuel cell system associated with three macrophytes

Rhizodeposits excreted by various macrophytes might lead to the potential discrepancy of microbial community distribution in constructed wetland coupled with microbial fuel cell (CW-MFC), which has been considered as main factors for the variations of bioelectricity generation during wastewater treatment. In this study, CW-MFC has been associated with three macrophytes (J. effuses, T. orientalis and S. validus) for domestic sewage treatment, also unplanted CW-MFC was performed as a control system. Macrophyte T. orientalis and S. validus can significantly strengthen the bioenergy output in CW-MFC. Highest current (94.27mAm−2) and power densities (21.53mWm−2) were obtained in CW-MFC planted with T. orientalis. Removal efficiencies of COD, NO3-N and NH3-N in CW-MFC planted with S. validus was respectively 5.8%, 7.2%, and 23.9% higher than that of unplanted system. Notably, the oxygen depletion in S. validus CW-MFC reactor during the dark cycle was higher that of other reactors. Results of high-throughput sequencing analysis showed that higher biodiversity was observed in rhizosphere than that of anode material, and the relative abundance of Desulfobulbus sp. and Geobacter sp. has been apparently promoted in the samples of rhizosphere. However, a higher relative abundance of electrochemically active bacteria (Proteobacteria) was observed on the surface of anode electrode material. In addition, microbes (Cytophagales, Clostridium sp., and Dechloromonas sp., and so forth) found in rhizosphere show a capability to decompose refractory contaminants. These contaminants and death roots in the upper part of wetland could be oxidized to fat acids, which may be used as the electrons acceptors for promoting the bioelectricity generation during wastewater treatment.